The human heartbeat, or cardiac cycle, represents one of the primary vital signs monitored by health care providers and members of the general public alike. Heartbeat, as used herein, refers to a complete heartbeat, or a set of heartbeats, from its generation to the beginning of the next beat; thus, it includes the diastole, the systole, and the intervening pause. The pace of the heartbeats, referred to herein as the heart rate, is a measure of cardiac cycles per time period. Heart rate is typically measured in beats-per-minute (BPM) as a measure of, on average, how many cardiac cycles occur per minute. The BPM measurement can be an average heart rate, measuring the average BPM over a sizeable period of cardiac cycles, or an instantaneous heart rate, measuring the BPM over a short period of cardiac cycles and extrapolating out the BPM.
Conventionally, the heart rate is measured using equipment such as an electrocardiogram by recording the electrical activity of the heart over a period of time using electrodes placed on the skin. This approach is a significant expense and requires invasive electrodes to be placed on a subject. Other conventional approaches include attaching a heart rate monitor to a subject, which typically includes a chest strap transmitter and a receiver. This approach is not particularly accurate and susceptible to noise, and in addition, requires the subject to place the transmitter under his/her clothes. Further types of strapless heart rate monitors allow the measurement of the heart rate with a wearable device, such as a wristwatch or finger clasp, by utilising an infrared sensor to measure the heart rate. However, such devices do not provide much detail and are not particularly accurate.